PURPOSE: To feed composition to reduce fats in abdominal cavity without reducing growing weight of domestic animal, or to strengthen quality of eggshell in case of chicken, by adding a fixed amount of a dithia derivative shown by the formula to a feed.

CONSTITUTION: A dithia derivative shown by the formula (R and R' may be the same or different lower alkyl group; n is interger of 0, 1, or 2; A is -CH2-, -CH=CH-, -CH2CH2-, etc.) is added to a feed. The composition applies to animals such as chicken, quail, cattle, pig, yellow tail, carp, and 10W2,000ppm of the compound is added to the feed such as maize, milo, barley, wheat bran, white fish meal, soybean cake, etc. Diisopropyl-1,3-dithiolan-2-indenemalonate, diisopropyl-1,3-dithiol-2-indenemalonate may be cited as the compound. Consequently, a protein amount in organism is increased, and quality of eggshell can be stregthened.